Sugar beet pectin is a natural high-molecular-weight polysaccharide derived from sugar beet (Beta vulgaris LINNE. var. raga DUMORTIER). Sugar beet pectin is composed of: a backbone of α-1,4-glycoside-linked poly-D-galactulonic acid; a side chain mainly comprising a neutral sugar, such as arabinose or galactose; and a proteinaceous moiety bound to the sugar chain. Sugar beet pectin has an average molecular weight of about 350,000 to about 550,000 g/ml, which corresponds to about 1.5 to 3 times the average molecular weight of ordinary citrus-derived pectin, and contains the side chain in a higher proportion than citrus-derived pectin. It is thus that sugar beet pectin is more nearly spherical than citrus-derived pectin. Furthermore, sugar beet pectin has a methyl esterification degree of 50% or more, and a total esterification degree of 85% or more, and is therefore categorized as a high methoxyl (HM) pectin.
Pectin is known to be used to prepare various emulsions (see, for example, Patent Literatures 1 to 3). However, when using citrus-derived pectin alone, whether it is a low methoxyl pectin or a high methoxyl pectin, sufficient emulsifying ability may not be exhibited. In contrast, sugar beet pectin has higher emulsifying ability than citrus-derived pectin, and can form an emulsion having a small particle diameter, even when used alone in a small amount.
However, it has been pointed out that emulsions prepared using sugar beet pectin do not always have good storage stability. To solve this problem, polymerization techniques that include a method of heating sugar beet pectin in the form of a powder (Patent Literatures 4 to 6), or a method of exposing sugar beet pectin to ionizing radiation in the presence of water (Patent Literature 7 to 9) have been reported. However, to use these methods, a special device that is usually not used in the production of sugar beet pectin must be used to control the temperature, humidity, etc. and problems such as insufficient emulsion stability improvement remain to be solved.